Field of the Invention
The present invention relates to an automatic transmission for a vehicle. More particularly, the present invention relates to a planetary gear train of an automatic transmission for a vehicle that may improve power delivery performance and reduce fuel consumption by achieving at least ten forward speed stages using a minimum number of constituent elements, and may improve silent driving by using a driving point positioned at a low engine speed.
Description of Related Art
Recently, increasing oil prices have caused vehicle manufactures all over the word to rush into infinite competition. Particularly in the case of engines, manufactures have been pursuing efforts to reduce the weight and improve fuel efficiency of vehicles by reducing engine size, etc.
As a result, research into reduction of weight and enhancement of fuel efficiency through downsizing has been conducted in the case of an engine and research for simultaneously securing operability and fuel efficiency competitiveness through multiple speed stages has been conducted in the case of an automatic transmission.
However, in the automatic transmission, as the number of speed stages increases, the number of internal components also increases, and as a result, the automatic transmission may be difficult to mount, the manufacturing cost and weight may be increased, and power transmission efficiency may be deteriorated.
Accordingly, development of a planetary gear train which may bring about maximum efficiency with a small number of components is important in order to increase a fuel efficiency enhancement effect through the multiple speed stages.
In this aspect, in recent years, 8-speed automatic transmission tends to be implemented and the research and development of a planetary gear train capable of implementing more speed stages has also been actively conducted.
A conventional automatic transmission of eight or more speed stages typically includes three or four planetary gear sets and five or six control elements (frictional elements), and thus mountability may be deteriorated due to increase of volume and weight.
In this regard, disposing planetary gear sets in parallel or employing dog clutches instead of wet-type control elements has been attempted. However, such an arrangement is not widely applicable, and using the dog clutches may deteriorate shift-feel.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.